The background of this invention involves digital scanners and software based methods. Presently, typical scanners provide very high optical resolutions and brilliant color depth. However, the superior imaging quality typically results in long scan times and slow imaging speeds.
The optical resolution of the images scanned by digital scanners is a function of the number of pixel capture sites (also called “photosites” or “pixels” in the electro mechanical sense) on the electro-mechanical sensor assembly in the scanner. Scanning is done in a Cartesian mode, i.e., a linear array of the pixel sites are mounted on a longitudinal bar; the bar is moved as a unit along a vertical path. Each pixel is a small area on the surface of the image sensor that captures the brightness of a single image area pixel of the image, with one scanner pixel for each image pixel in the digital image. In that way, the number of pixels on the scanner's image sensor bar determines the horizontal optical resolution. The distance the bar advances between acquisitions (also called “shots”) determines the vertical resolution. For example, a scanner with a resolution of 600 dots per inch (dpi)×1200 dpi has 600 pixels on its sensor bar which moves 1/1200 of an inch between each scan shot. Together, the horizontal and vertical resolutions constitute the optical resolution and determine the level of detail that the scanner can capture.
To increase the resolution of a scanner, the number of pixel sites on the scanner head (the “horizontal” or transversely aligned bar containing the linear array of CCD or CIS photosensitive elements) must be increased, the distance the scanner bar mechanism moves between acquisition shots (the “vertical” or longitudinal resolution) must be decreased, or some combination of the two. Current technology offers two basic types of pixels: CSI and CCD (other types of elements may become available in the future). There is a technological constraint on the horizontal resolution, which is determined by the number of pixels arrayed on the bar due to their physical size and how closely they can be positioned to one another. To increase the vertical resolution, digital scanners must move smaller and smaller distances between scans. Since the illumination lamp output changes over time, and the length of exposure depends on brightness and dpi, the scanner head is ordinarily calibrated from time to time (often at each scan) to control the length of pause for exposure at each acquisition shot. CSI element-containing scanner bars are typically slower as they require more light per exposure, and the slow down is more pronounced at low resolution.
Typical digital scanners today provide vertical optical resolutions of 1200 to 4800 dpi. Thus, the scanner mechanism moves 1/1200 to 1/4800 of an inch between each single line shot or scan. This process generates a large quantity of digital data (large image data file), which needs to be transferred to the host system (computer). Because of limitation in the communication speed with the hose, high-resolution scans take a long time, with typical scanners on the market presently taking two minutes or more to complete a single pass at the highest resolution for the full length of the scanner platen (typically 11.69″). Current CCD scanner bars employ around 3×10,400 pixels (the “3” refers to the colors R, G, B), and scanner bars having higher resolutions are within the scope of this invention. The net actual attainable resolution is not determined only by the pixel density, but in large part is determined by the optics of the scanner. For example, most scanners rated at “1200 dpi” resolution are limited to 600 dpi or less due to optical constraints.
The high-resolution scan is slower than preview scanning, the rate depending on the resolution. The scan bar moves at a speed proportional to the resolution, regardless of whether the image is in B&W, grayscale or color, and how fast the data can be transferred to the host. The scan speed is dependent on the resolution, color/ grayscale/B&W, and transfer-to-host speed, but is independent of the area of the image being scanned. That is, if nothing is on the platen, even though the scanner head sees “white”, where high resolution is the selected scan mode, the scan speed is slower than if preview or low resolution is selected as the scan mode. Although some scanners may have a relatively fast return feature in which the non-scanning return to the start position is faster than scan, that return time is still wasted wait time. CIS heads are slower than CCD, and for large color photo images, the data files can be very large, with consequently slow transfer. For a CCD head scanning an 8½″×11″ image on a standard 8.7×11.69″ platen, the scan times are set forth in Table 1 below.
TABLE IScan Time at Various ResolutionsScan Time in Seconds, for8.5″ × 11″ ImageResolution, DPIB & WColor10078300203060030120
Return speed typically ranges from 3½ seconds to 15 seconds, depending on the scanning motor type and the return speed is set, not variable or programmable. CIS head return speeds are slower.
Image Cropping:
In order to reduce scanning time and to reduce file size, present scanner manufacturers allow users to either manually, or automatically, make a single, low resolution scan, e.g., at 72-100 dpi. An example of current cropping hardware and software technology is shown in Santos, U.S. Pat. No. 4,837,635 (Hewlett-Packard). The image created from the preview scan by the digital scanner is rectangular in shape and consists of an image of everything on the flatbed scanner, e.g., the document being scanned as well as all the blank space around that document. The software or firmware of the systems creates a low-resolution image, and either the user or an automatic cropping algorithm selects the desired region of the image. The user or cropping algorithm draws a box or “lasso” around the image and then transmit to the scanner the instruction to scan, at a high resolution, the area marked off by the crop box or lasso. While the user or cropping algorithm selects the region of the low-resolution image to rescan, the scanner bar returns to its normal starting position in order to prepare to make the next, high-resolution, scan, e.g., 300, 600, 1200 or more dpi. Cropping and B&W scanning reduces data transfer time, cropping because there is less total data, and B&W because it is 1 bit vs 24 bit data for color. With automatic cropping algorithms, the cropping action may take a fraction of a second, but currently available scanners take time for the scan bar to return to its starting position to begin the high-resolution scan.
A serious disadvantage of the present scanning/cropping technology arises from the number of passes that the scanner bar must take in order to acquire and render the final high-resolution, useable image on screen for saving to a data file. Typically, currently available scanners take 4 passes per image: 1) Low resolution preview/crop; 2) return; 3) high resolution acquisition scan; and 4) return. Where there are multiple images to acquire, this process takes a very long time, and adds significant cycle wear to the scanner hardware.
There is thus a significant need for a scanning system that automatically crops and acquires high resolution images in short, fast scanning cycles that permits faster through-put and reduced component cycle wear.